1. Field of the Invention
The present invention relates to a projector which performs two-dimensional scanning using a light beam to project a two-dimensional image on an object. In addition, the present invention relates to an image projection method, and a head-up display device using the projector.
2. Discussion of the Background
Projectors including a lighting optical system, which includes a light source, a spatial light modulation device for forming a light image using light emitted from the light source, and a lens for projecting the light image, have been proposed and commercialized. With the spread of such projectors, an increasing need exists for small-size projectors. In order to fulfill such a need, small-size projectors using a LED or LD as a light source have been developed. Such projectors are used for small-size electronics devices such as mobile phones.
In addition, instead of using a spatial light modulation device, published unexamined Japanese patent applications Nos. 2001-154263, 2001-174919, 2005-309221 and 2007-199251 have disclosed light scanning methods in which a light beam emitted from a light source is two-dimensionally deflected using a light deflector to perform two-dimensional scanning on a projection object so that the scanned light beam is focused on the surface of the projection object. A person can observe such a scanned two-dimensional image as an image due to the afterimage effect.
Such light scanning methods typically use polygon mirrors, galvanometer mirrors, MEMS mirrors prepared by using a MEMS (Micro Electro-Mechanical Systems) technique, etc., as light deflectors.
FIG. 1 illustrates a background projector using a light scanning method. Referring to FIG. 1, the background projector includes a controller 1, and a light scanning device 2 as main components. The controller 1 includes a light amount controller 3, which controls the light amount of light emitted from a light source of the projector on the basis of the light amount control data corresponding to pixel data (i.e., luminance data G(i,j)) of an original image input to the light amount controller, and a light deflector drive controller 4, which controls the light deflection direction of a light deflector (e.g., galvanometer mirrors) on the basis of another pixel data (i.e., positional data) for the original image input to the light deflector drive controller.
The light scanning device 2 includes a light source 5 emitting a light beam P, a divergence angle converter 6 (e.g., projection lens), and a light deflector 7. The divergence angle converter 6 changes the divergence angle of the light beam emitted from the light source 5 so that a focused light spot S is formed on the surface of a projection object Sc (e.g., screens).
The light deflector 7 deflects the light beam emitted from the divergence angle converter 6 in a first scanning direction and a second direction perpendicular to the first scanning direction to form the focused light spot S at a pixel position (i′,J′) corresponding to the position (i,j) of the pixel of the original image. The light deflector drive controller 4 performs two-dimensional control on the light deflector 7 on the basis of the positional data (i,j) so that the focused light spot S is formed at the pixel position (i′,J′) corresponding to the pixel position (i,j). The light amount controller 3 controls the light amount of light emitted from the light source 5 on the basis of the light amount control data corresponding to the luminance data G(i,j) for each pixel of the original image.
Such a projector has a projection image deterioration problem in that qualities of projected images deteriorate depending on the properties of the projection optical system of the projector including the divergence angle converter 6 and the light deflector 7. For example, when an image is projected on the screen Sc using a movable mirror such as galvanometer mirrors as the light deflector 7, a need exists for short-range image projection or high resolution image projection. In this case, it is necessary to increase the slanting angle (amplitude of the movable mirror), i.e., a deflection angle θ illustrated in FIG. 1, while moving the mirror at a high speed. In addition, it is necessary to reduce the weight of the movable mirror by thinning the mirror and/or decreasing the area of the mirror in order that the movable mirror can be stably moved.
However, when the movable mirror is thinned, the mirror tends to be greatly bent when moved, thereby deteriorating the qualities of the focused light spot S, resulting in deterioration of resolution of the projected image. In order to decrease the area of the movable mirror is decreased, the size of the light beam P emitted from the light source 5 has to be decreased. In this regard, if the area of the movable mirror is small, diffraction phenomenon occurs, thereby deteriorating the qualities of the focused light spot S. Therefore, the area of the movable mirror has a lower limit.
Namely, as the distance of a pixel at a position (i′,j′) from a center O1′ of the projected image, which corresponds to a center O1 of an optical axis of the projection optical system, becomes longer, the focused light spot S has a larger diameter or greatly deforms. Thus, such a background projector as projecting an image by scanning the screen Sc serving as a projection object with a light beam (i.e., focused light spot S) causes the projection image deterioration problem depending on the properties of the projection optical system thereof including the divergence angle converter 6 and the light deflector 7.
Because of these reasons, a need exists for a projector or an image projection method, which can solve the projection image deterioration problem caused by a projection optical system, without using any additional optical element.